Method for carbonizing fibers



Sept. 115 1962 w, F. ABBOTT METHOD FOR CARBONIZING FIBERS Filed Nov. l2,1959 l//LL//JM ,055077 INVENToR.

o-W 54X 706/145' VS United States Parent fornia i t Filed Nov.` 1 2',1959, Ser. No. 852,580 8 Claims. (Cl. 252-421) This applicationisV a'continuation-impart of my prior, co-pending application Serial No.569,391, filed March 5, 1956, entitled Method for Carbonizing Fibers,and Articles Produced Therefrom, now abandoned.

This' invention relates to Vfibrous materials and has particularreference to a process for carbonizing fibers and to articles producedtherefrom.

One of the primary objects of this invention is to provide a process forthe production of carbon in fibrous formv having a highV intrinsic liberdensity and good tensile strength. While fibers of carbon are notbasically new, carbon fibers heretofore produced have been so weak instructure that they could not resist even slight mechanical forceswithout breakage or disintegration. The present invention provides forthe first time bers substantially of car-bon which are su'fiicientlystrong to retain theiriibrous form upon being subjected to mechanicalforces.

Another object of this invention is to provide a hard, high densitycarbon in the form of tine fibers, the fibers being clean and' strongbecause of the high density, yet flexible and resilient due to the smalldiameter of the fibers.

Another object of this invention is to provide a process for theproduction of carbon fibers having a wide rangel ofiber diameter andother characteristics for use in varied specific applications.

Another object of this invention is to provide a carbon fiber which iscapable of being activated to `a high level While -still .retaining 4aconsiderable part of its original strength, the activated fiber havingadsorption characteristics equal on a weight basis to conventionalactivated carbon in granular form. Granular activated carbon is Wellknownjin industrial applications, but is limited to use' applications'which provide means to contain the carbon granules. Activatedcarbonfibers of the present invention e'xtendthe use of carbon toclothing, masks, andiilters of fiber construction.

Other objects and advantages ofthe invention,` it is believed, will bereadily apparent 4from the following detailed description o f preferredembodiments thereof when readin connection with the accompanyingdrawings.

In the drawings:

The single FlGURE is a diagrammatic view illustrating the apparatusrequired to carry out the process of this invention on a small scale.

Briefly, this invention comprehends within its scope the discovery thatcertain synthetic fibers may Ibe car-4 bonized by carefully controlledthermal decomposition to produce a dense, strong carbon fiber, Thechoice of rawmaten'als is limited to synthetic fibers of thenonthermoplastic type, which do nottend to melt or how on heating andhence retain the fibrous form when heated to the ldecomposition point.

Natural fibers, `such as cotton, for example, are not suitablefor thepurpose of this invention. Although such fibers may be carbonized, theyare weakand therefore are unsatisfactory for practical use in the formof carbon fibers.

lthas been found that a regenerated cellulose fiber, such as viscoserayon, cuprammnium rayon and'saponified acetate rayon, is a particularlysuitable raw Amaterial foi accomplishing the endsofwthepresentinvention.

HCC

The present process comprises heating' the raw fiber material in aninert, oxygenfree atmosphere to a temperature suiciently high to bringabout substantially complete Vthermal decomposition of the non-carboncorrstituents ofthe material, great care being taken to confL trol therate of temperature risesiohthat gasificaticn is slow to prevent fiberrupture by rapid dec'ompos'itiri.`

4It has been discovered that a critical temperature f angfel of fromabout 250 to about 5002" E ex'ists for thedej sired carbonization of theraw regenerated cellulose tibiA It is in this range that theV major partof the ca rbo-r'iiii-L tion takes place. It is extremely important' thatthe rate of temperature rise throngh this temperature range becontrolled so that the weight yield of c'arbo 1 `1` fiber will begreater, preferably, than 45 percent' o\f the c bon content of theoriginal raw regenerated cellulose, and so that the tensile strengthofthe resultant'carboniibei" will be at least 5,000 p. s.i. Thetemperature rise through thi-s range for a single fiber, for example,should take place uniformly in not less. than Srininuts and preferablyover a period of one hour so as to preventexcessively fast gasification,s uch as would otherwisedamag'e the fiber. In actual practice,utilizinga mass .of fibersthe time required to raise the temperature o f4the entire nia'ss of fibers through this range will exceed thetimerequired for an individual fiber according .tothe heat, tran sfe r char acteristics of the particular, equipment employed and the volumeofthe mass offibfers-v The gaseous decomposition products givemoffdu theheating, operation can themselvesprovide the inert, oxygen-freeatmosphere if properly contained In` ,order; to avoid brittl eness inthe product, theffiberddiameteri of the raw materials s'hould be'` lessthan abou;t 2 0 O microns. Preferably, the'ber diameter is lessl than100 rnicrons.

The raw materials may, be` tijeateddnthefqrm offlco'n tinuousmono-filamentain ghyforrr'rv of shortflerigth .or staple fibers, the forin oflyarn" of, woven webs; or. any other suitable fiber for '1r`1.Continuous mo'no-fila-, ments or yarns are preferredfsince they can be,contin ously treatedj by passag e through a suitable furnace or otherheating apparatn's. ,V ,i i

'l`l 1econtiui.i`o`usprocess` may `b 4 furnace having a p reheatsect1onf..fol lowed..b -pheric trap, .acarboniziing section aridaicoolthrough, which the fiber, is drawn.,4` 'lghe roller .for the fibershoulclfbe'ofi ceramic material, `an i aterial is preferably. supporit-edA andwguid A furnace onk a guide belt or beltsoi g1 1 artz.glassclcjthn Inasmuchas the fibers undergo. shrinkageofffrorn to 35%during carbonization, provision must, be, made for such shrinkage byproviding for multiple-driver gf. quartzbelts in the carbonizatipn zjonef l`he cog l ing. s ec tioni may comprise water j acketedheattransfergplates,

The process may alsobe `carried out batchwiseyiu-. suitable furnaceprovided With adequate temperature controlrneans. ,y ff( Produtsrrodudby the abqvezdesribedthernial der composition processhave a .wide,se9pe;of industria1 u s es., Thavbon .fibers are strong, yethighly iexibleand man be readily fabricated into the desired form or assembled withother components foruse f-huS, Coritinuous carbon filaments maybe.wover1 into ,yarn and/or clothgfor then, malinsulation, filtrationapplications nad., the .like..:i.Th.e. yarn, cloth, or staple carbonfiberstghaving sufficient strength to provide a sc lfzsupporting mass offibers, may be formed into mats or padsforsimilar uses. Also, the carbonfibers in yarn, or staple form mayabemsedfas a catalyst 0r` CatalystCarrier, and;L as a eaulkng mateal for; specialized applications. Otherindustrial` applications will readily present themselves to thoseskilled in the art.

If desired, the brous raw material may be formed before carbonizationinto mats, pads, orY continuous webs of low bulk density and having ahigh degree of shape retention by bonding the bers together with asuitable thermosetting resin such `as urea formaldehyde. The resinshould be applied at a low viscosity such that cross-ber cementingoccurs without the deposition of excessive or thick resin masses.v Anyextensive thickening ofthe ber diameters or the formation of nodules ofresin on the bers `is undesirable and produces brittle Vsections in thenished product. Preferably,the resin bond lm is of the sameorderofmagnitude as the ber diameter. The cured,resinbonded ber mats or padsare carbonized in accordancewithV the above-described process to producecarbon-bonded, carbon ber mats or pads suitable forense in air lters, asthermal insulation and the like. e

V' It isjwithin the scopeofqthis invention to provide the carbon` bersVwithV coatings of various types, applied either before or aftercarbonization. Such coatings may include oxides for variouspurposes,'i.e., MgO, ZnOg, etcQ, forimp'roved reproong, to minimize-theneed to protect the material from-oxidizing atmospheres when used as lathermal insulation; Fe203, Cr2O3, A1203, as catalyst surfaces forcatalytic reactions utilizing `the carbon ber as the carrier; CuO, CuzO,etc., for inversion of the selective adsorption characteristics toprovide specic adsorption properties; andappropriate oxides to changethe black color ofthe carbon bers.

The above and other surface coating materials may be introducedprior toor during regeneration and ber formation. This simplies the coatingprocess and produces more thorough and-uniform coatings, more impertothe ber. It has been found that during the'carbonization process the rawmaterial undergoes a change'from an elecnace on ceramic blocks 12 was aset of three rectangular iron pans 14, 15 and 16 of progressivelyincreasing size.V The pan 14 measured 19" in length, 10 in width and 6in depth; the pan 15 measured 20 X 11" x 61/2; and

can Viscose Co., 5.5 denier; length, 5"-7; qual., A;

type, var. reg.; lustre, brt.; sym., 1432) to prevent pack-` ing.V Pan14 wasthen. covered with pan 15 and the two pans inverted and thencovered with pan'16. 'Ihe furv Vnace was preheated to 300 F. for aboutl5 minutes and vious coatings, and coatings with a greater degree ofbond the assembly of the three pans put into the center of the furnaceon ceramic blocking to permit uniform movement of air. The furnaceandcontents were then heated slowly through the gasication stage (300-500F.) for 21A hours. The temperature was then allowed to rise to 1000 F.to drive o Vthe gases, the lfurnace then turned olf and the batchallowed to cool for 18% hours. v

The carbon bers producedV had a `tensile strength of l 10,000 p.s.i. anda weight yieldkof 52% of the carbon content of the raw regeneratedcellulose bers. Y

The followingrexample vdescribes the production of activated kcarbonwool bers by the batch method:

f I ExampleVV vThe apparatus described in ,Example 1 was utilized with lthe addition of a lengthY of 1i-inch steel tubing 30 welded throughoneendV of thepan 15 andV to the bottom, the tubing being provided Witha plurality (-about 6 in this case) of l 1zfinch holes 31 equally spacedinside the pan length. The tubing passed through the furnace'port- 11.`

uctrnay be made to exhibit variable specic resistance.

, SuehV materials are useful in electronic applications suchV asinmaking sensing elements, transducers, conductivity devices, andthelike.`

Carbon bers produced by the present carbonization method have verylowadsorption'capacity. These same bers jmay, however, befactivatedV toprovide saturation adsorption capacities fori carbon tetrachloride, forexam! ple, of E10-50% by Weight of the activated carbon ber, whilestillretaining a higrhproportionjof the strength properties ofthe unactivatedcarbonized ber. It has Y been found that the vunactivated carbonizedbers may be activated Vbyjreattion with steam at temperatures from Y1Z00 to 1800 F. ThisV is( the well knownactivation process whichhasheretofore, been, applied to vgranular carbon materials'. 'Y Theactivation process may be carried out continuouslyon continuous lamentsby introducing a steam ret action? chamber immediately prior `to 'thecooling ,sectionV Y' carried out oni a small-scale batch operation, butitis to be understood that'theinvention-is not to be liimted to thedetails set forth: e

-Examplel j The apparatus is shown diagrammatically inthe drawingandincludes a 4 bur`ner, gas-redbox kiln furnace 10 provided with a sideport 11. Mounted inside the fur- A S-gallon bottle 39 of distilled waterwas positioned on top of the furnace'andprovided with a supply tube 40conl nected to the tubing 50.V A stop-cock 45 was also provided in thetube 40.

The carbonization step vof this examplewas identical to that of Example1, except that here, following the 2%- hour carbonization step, thetemperature of the carbon bers was raised to 1450" F., and maintainedthere for about'2 hours, during which time about 5 gallons of distilledWater from the bottle 39 wasV- slowly fed by gravityk into the tubing30. Steam was thus -forced out of the holes- 31 and through thecarbonized bers to activate the same. Atgthe end ofthe two-hour period,Vthe batch was dried by lowering the temperature to about 500 F. forabout l5V j minutes. The furnace was then allowed to cool for about 18%hours as in Example 1. The activated carbon bers yF. for 21/2 hours. Thetemperaturen/as then raised` to l l000 F. to drive oi gases from thefurnace; The batch of ycarbonized bers was Vthen permitted to cool toroom temperatures over a period of approximately 18 hours.

VThe carbon bers thus 'produced were tested and revealed a tensilestrength of 8,000p.'s.i. and a Weight yield equal to 50.4% of the carboncontent of the raw cupram? monium rayon bers. p

' Example 4 e Again, utilizing the apparatus described in connectionwith Example 1, a 1.5 pound batch of 1 denier saponied acetate rayonbers was carbonized yby slowly heating the same through a temperaturerange of 250". F. to 500 F.

for 21/2 hours. The temperature was then raised to 1000 F. and the batchallowed to cool to room temperature over an 18 hour period. Theresultant carbonized bers were tested and revealed a tensile strength of11,200 p.s.i. and a weight yield equal to 51.7% of the carbon content ofthe original saponied acetate rayon bers.

Further tests and experiments in connection with single bers ormono-laments of these materials reveal that the rate of increase intemperature through the critical range of -from about 250 F. to about500 F. should be accurately controlled, so that the increase intemperature from 250I F. to 500 F. will consume a period of time of atleast 8 minutes. If the temperature rise is attained in a time shorterthan 8 minutes, the tensile strength and weight yield of the resultantcarbonized ber will be materially reduced.

Having fully described my invention, `it is to be understood that I donot wish to be limited to the details set forth, but my invention is ofthe full scope of the appended claims.

Having thus described my invention, what I claim is:

l. A process for the production of a carbon ber comprising the steps ofheating viscose rayon ber in an inert atmosphere through a temperaturerange of from about 300 F. to about 500 F., said heating requiring atleast 30 minutes to attain said 500 F. temperature.

`2. A process for the production of a carbon ber comprising the steps ofheating viscose rayon ber in an inert atmosphere through a temperaturerange of from about 300 F. to about 500 F., said heating requiring abouttwo hours to attain said 500 F. temperature.

3. A process for the production of a carbon ber comprising the steps ofheating viscose rayon ber in an inert atmosphere through a temperaturerange of from about 300 F. vto about 500 F., said heating requiring atleast 30 minutes to attain said 500 F. temperature, and subjecting theber thus produced to the action of steam at an elevated temperature toactiva-te the same.

4. A process `for the production of a carbon ber comprising the steps ofheating viscose rayon ber in an inert atmosphere through a temperaturerange of from about 300 F. to about 500 F., said heating requiring abouttwo hours to attain said 500 F. temperature, and subjecting the ber thusproduced to the action of steam at an elevated temperature to activatethe same.

5. The method of making a carbon ber which cornprises heating anon-thermoplastic, regenerated cellulose ber in an inert atmospherethrough a temperature range of `from approximately 250 F. toapproximately 500 F., said heating requiring at least 8 minutes toattain said 500 F. temperature.

6. The method of making a carbon ber which comprises heating anon-thermoplastic, regenerated cellulose ber in an inert atmospherethrough a temperature range of from approximately 250 F. toapproximately 500 F. in a time period of not less than 8 minutes; andsubjecting the ber thus produced to the action of steam at an elevatedtemperature to activate the same.

7. The method of making a carbon ber having a tensile strength of atleast 5,000 p.s.i. which comprises heating in an inert atmosphere aregenerated cellulose ber selected from the class consisting of viscoserayon, cuprammonium rayon and saponied acetate rayon, through atemperature range of from about 250 F. to about 500 F., the increase ntemperature yfrom about 250 F. to about 500 F. being accomplished in notless than 8 minutes.

8. 'I'he method dened in claim 7 including the further step ofsubjecting the thus heat-treated ber to the action of steam at a furtherelevated temperature to activate the same.

References Cited in the le of this patent UNITED STATES PATENTS2,925,879 Costa et al Feb. 23, 1960 FOREIGN PATENTS 11,997 Great Britain1886

1. A PROCESS FOR THE PRODUCTION OF A CARBON FIBER COMPRISING THE STEPSOF HEATING VISCOSE RAYON FIBER IN AN INERT ATMOSPHERE THROUGH ATEMPERATURE RANGE OF FROM ABOUT 300*F. TO ABOUT 500*F., SAID HEATINGREQUIRING AT LEAST 30 MINUTES TO ATTAIN SAID 500*F. TEMPERATURE.